Theory 44/Terraces/Threshold lens
Walls Fail on a Storm Ratio
The claim
Terrace wall failure occurs above a threshold in the ratio of rainfall intensity to drainage capacity, so a modest storm on a blocked drain does more than a large one on a clear drain.
01Mechanism
Water accumulates behind the wall when inflow exceeds drainage; the ratio sets the pressure on the structure.
02Prediction
Failure should track the ratio.
03Refutation
Failure tracking rainfall would remove drainage.